Manzo sat in front of a camera on July 22 for a deposition in Staub's ferocious legal war with her ex-husband Kevin Maher ... who's demanding $10 million for alleged defamation.

During the depo -- Manzo claims Staub told stories about her alleged abusive past with Maher ... including one situation where Maher allegedly raped Staub on broken glass, killed her dog and "inserted a pistol up her vagina."

Staub has claimed Maher has "no evidence" she ever made those statements about him.

Best part of the tape -- Manzo is asked about Staub's "propensity for truthfulness" ... and Caroline just unloads.